Objective 1.8

Question 1

Concept: IPv6 Address Size and Format

How many bits and what is the format?

Answer 1

An IPv6 address is 128 bits long.

It is written as eight groups (or “hextets”) of four hexadecimal digits, separated by colons.

Example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334

Question 2

Concept: IPv6 Abbreviation Rule #1

Leading Zero Omission

Answer 2

Leading zeros within any hextet can be omitted.

• 0db8 becomes db8
• 0000 becomes 0
• 0370 becomes 370

Example: 2001:db8:85a3:0:0:8a2e:370:7334

Question 3

Concept: IPv6 Abbreviation Rule #2

The Double Colon ::

Answer 3

A single, contiguous group of all-zero hextets can be replaced by a double colon (::).

IMPORTANT: This can only be used ONCE per address.

Example: 2001:db8:85a3::8a2e:370:7334

Question 4

Scenario:

Abbreviate the following IPv6 address using both rules:

fe80:0000:0000:0000:02a1:12ff:fe34:45a1

Answer 4

fe80::2a1:12ff:fe34:45a1

The four all-zero hextets are replaced by :: and the leading 0 in 02a1 is omitted.

Question 5

Concept: Anatomy of a Unicast IPv6 Address

What are the three parts?

Answer 5

An IPv6 unicast address is typically divided into three parts:

1. Global Routing Prefix (first 48 bits): The “network” portion, assigned by an ISP.
2. Subnet ID (next 16 bits): The “subnet” portion, which you control for your internal networks.
3. Interface ID (last 64 bits): The “host” portion, uniquely identifying a device on the subnet.

Question 6

Address Type: Global Unicast

Prefix / IPv4 Analogy:

Answer 6

Prefix: Typically starts with 2000::/3.

IPv4 Analogy: A public IPv4 address. It is globally unique and routable on the internet.

Question 7

Address Type: Link-Local

Prefix / IPv4 Analogy:

Answer 7

Prefix: Always starts with fe80::/10.

IPv4 Analogy: APIPA (169.254.x.x). It is automatically self-assigned, required on every IPv6 interface, and is not routable. It is used only for communication on the local network segment (e.g., neighbor discovery).

Question 8

Address Type: Unique Local

Prefix / IPv4 Analogy:

Answer 8

Prefix: Starts with fc00::/7 (most commonly fd00...).

IPv4 Analogy: A private IPv4 address (10.x.x.x, etc.). It is used for internal networking and is not routable on the public internet.

Question 9

Address Type: Anycast

Concept / Use Case:

Answer 9

Concept: One-to-the-nearest communication. A single Anycast address is assigned to multiple devices in different locations. Packets are routed to the device that is geographically or topographically closest.

Use Case: Root DNS servers, Content Delivery Networks (CDNs).

Question 10

Assignment Method: SLAAC (Stateless Address Autoconfiguration)

How it Works:

Answer 10

A device listens for a Router Advertisement (RA) message from a local router.

It takes the network prefix provided in the RA and combines it with its own Interface ID (often generated from its MAC address via EUI-64) to create its own IP address.

Question 11

Assignment Method: Stateful DHCPv6

How it Works / When to Use:

Answer 11

How: Works like DHCP for IPv4. A central DHCPv6 server assigns a device its IP address and all other configuration options (DNS, etc.). The server tracks the status (the “state”) of each client.

When: Use when you need tight administrative control over IP address assignment.

Question 12

Assignment Method: Stateless DHCPv6 (“SLAAC with DHCPv6”)

How it Works / Purpose:

Answer 12

How: A hybrid method. The device uses SLAAC to get its own IP address, but it contacts a DHCPv6 server to get other information only, such as the DNS server address.

Purpose: This is very common. It provides the automation of SLAAC while still allowing for centralized control of key options like DNS. The server does not track IP leases, making it “stateless.”

Question 13

Comparison: SLAAC vs. Stateful vs. Stateless DHCPv6

Key Differentiator:

Answer 13

• SLAAC: Provides IP address only. No DNS.
• Stateful DHCPv6: Provides IP address AND other options (DNS). Server tracks everything.
• Stateless DHCPv6: Client gets its own IP via SLAAC. Server provides other options (DNS) but does NOT track IP addresses.

Question 14

Transition Mechanism: Dual Stack

Concept / Key Fact:

Answer 14

Concept: A device’s network interface card (NIC) runs both the IPv4 and IPv6 protocol stacks simultaneously. The device has both an IPv4 and an IPv6 address.

Key Fact: This is the most common and preferred method for transitioning to IPv6. It allows the device to communicate natively with both IPv4 and IPv6 hosts.

Question 15

Transition Mechanism: Tunneling

Concept / Analogy:

Answer 15

Concept: Encapsulating IPv6 packets inside of IPv4 packets. This allows IPv6 traffic to traverse an IPv4-only network infrastructure.
Analogy: Putting a letter with a new address type (IPv6) inside a standard, old-style envelope (IPv4) to get it through the existing postal system.